270. Performance of Early-Weaned Beef Calves Grazing Annual Ryegrass Under Different Concentrate Supplementation Strategies.

Abstract The objective of this study was to evaluate the effects of concentrate supplementation levels and delivery strategy on the growth performance of early-weaned beef calves grazing annual ryegrass (Lolium multiflorum). Three experiments were conducted at the UF/IFAS Range Cattle Research and Education Center, Ona, FL, from February to April 2022, 2023, and 2024. In 2022, treatments were concentrate supplementation at 0.75 or 1.0% of BW. In 2023, calves received concentrate at 0.5 or 0.75% of BW. In 2024, treatments were a fixed supplementation level (0.75% BW) or a stair-step strategy consisting of 0.5% BW in February, 0.75% BW in March, and 1.0% BW in April. In each experiment, 32 Angus crossbred calves (94±21 d of age) were assigned to 8 annual ryegrass pastures (0.3 ha; 4 calves/pasture), and treatments were distributed in a randomized complete block design with 4 replicates. Concentrate (18.9±0.8% CP and 75±3.0% TDN) was fed daily, herbage mass and forage nutritive value were monitored at 14-d intervals, and calves were weighed at 28-d intervals to determine average daily gain (ADG). There was no difference between treatments within years in herbage mass (HM), herbage allowance (HA), crude protein (CP), and in vitro digestible organic matter (IVDOM), averaging approximately 1846 kg DM/ha, 1.0 kg DM/kg BW, 26%, and 75%, respectively. In 2022, there was a supplementation level effect as calves receiving 1.0% BW had greater ADG than those receiving 0.75% BW (0.68 vs. 0.76 kg/d; P = 0.03). In 2023, there was no difference (P = 0.35) in ADG for calves receiving 0.5 or 0.75% BW (mean = 0.72 kg/d). In 2024, calves supplemented at a fixed rate (0.75% BW) or under a stair-step strategy had similar ADG (mean = 0.73 kg/d; P = 0.73). There was a month effect on ADG in all three years (P < 0.05). In 2022, ADG increased from February (0.70 kg/d) to March (0.95 kg/d) before declining in April (0.52 kg/d). A similar pattern was observed in 2023 (0.84, 1.00, and 0.32 kg/d for February, March, and April, respectively), whereas ADG was similar between February (0.82 kg/d) and March (0.81 kg/d) in 2024 but decreased in April (0.54 kg/d). Across experiments, calves supplemented at 0.5, 0.75, or 1.0% BW, and managed under a fixed supplementation level or stair-step strategy, had similar overall ADG during the three-month grazing period. These results indicate that decreasing concentrate supplementation level from 1.0 to 0.5% BW may be a viable management practice to reduce the cost of developing early-weaned beef calves grazing annual ryegrass under adequate forage availability, and that stair-step strategy may not increase the performance of early-weaned calves grazing annual ryegrass.